Security switch

ABSTRACT

The present disclosure relates to optical switching devices and switch modules that are designed for long-term security monitoring of high-value infrastructure access entry points. Embodiments in accordance with the present disclosure include optical switches based on fiber-Bragg gratings whose operating wavelengths are based on the presence or absence of magnetic coupling between an embedded permanent magnet and an external element. By monitoring the spectral position of the operating wavelengths and/or the magnitude of a light signal at the operating wavelengths, the state of the magnetic coupling can be determined and used as an indicator of whether the security switch has been actuated.

STATEMENT OF RELATED CASES

This case is a continuation of co-pending U.S. patent application Ser.No. 16/107,749, filed on Aug. 21, 2018, which claims priority to U.S.Provisional Patent Application Ser. No. 62/548,035 filed on Aug. 21,2017 (Attorney Docket: 3038-004PR1), each of which is incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates to switches in general, and, moreparticularly, to optical switches.

BACKGROUND

The area of security has received a great deal of attention in recentyears due to the need to protect infrastructure and other high valueassets. Part of this protection often includes alarming doors, windows,access panels, server doors, manhole covers, and other points of entry.There are many traditional switch designs that have been successfullyemployed to address many of these applications in the past; however,prior-art switches have several disadvantages, such as: sensitivity toelectrical noise in their environment; susceptibility to corrosion,which limits where they can be located; an inability to operate overlong distances, incompatibility with explosive environments, anddifficulty in detecting tampering.

A security switch that mitigates some or all of these disadvantageswould be a significant step forward in the state of the art.

SUMMARY

The present disclosure enables optical switching devices that overcomesome or all of the disadvantages of the prior art. Switches inaccordance with the present disclosure are designed for long-termsecurity monitoring of high-value infrastructure entry points.Embodiments in accordance with the present disclosure are particularlywell suited for use in remote locations, in electrically noisyenvironments, and/or in explosive environments, as well as in moreconventional deployments.

An illustrative embodiment in accordance with the present disclosure isa switch that operates without the need for electrical power at themodule and that optically communicates with a potentially highly remotebase station. The illustrative switch includes an optical fiber thatincludes a pair of fiber-Bragg gratings (FBG). Each FBG is held betweena fixed attachment point and a movable attachment point such that thefiber portion containing the FBG is under tension. The movableattachment points are mechanically coupled with a pivot assembly thatcan rotate about a rotation axis. The pivot assembly includes a bearingthat is concentric with the rotation axis and a permanent magnet locatedin close proximity to an outer wall of a housing that encloses theentire assembly. When an external element comprising ferromagneticmaterial (e.g., metal, a permanent magnet, etc.) is in close proximityto the outer wall, the permanent magnet is drawn toward the wall,thereby giving rise to a rotation force on the pivot assembly such thatthe pivot assembly rotates slightly about the rotation axis. Thisrotation increases the tensile strain in one FBG while simultaneouslyreducing the tensile strain in the other FBG. As a result, the spacingof the FBG elements changes in substantially equal and opposite fashion.This gives rise to an equal and opposite change in the operatingwavelengths of the FBGs. By monitoring the separation between theseoperating wavelengths, a change in the position of the external elementrelative to the outer can be detected.

In some embodiments, the pivot assembly includes two permanent magnetslocated on either side of the bearing such that the magnets are proximalto opposite outer walls. In such embodiments, the switch can be used todetect a change in the position of an external element relative toeither outer wall.

In some embodiments, only one FBG is included and the position of theexternal element is detected by detecting a step function in thewavelength response of the FBG.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B depict perspective and top views, respectively, of a switchmodule in accordance with an illustrative embodiment in accordance withthe present disclosure.

FIG. 2 depicts operations of a method for forming a security switch inaccordance with the illustrative embodiment.

FIG. 3 depicts a cross-sectional view of a representative FBG portion.

FIG. 4 depicts operations of a method for monitoring an access point inaccordance with the illustrative embodiment.

FIG. 5 depicts a schematic drawing of a top view of a switch module inaccordance with an alternative embodiment in accordance with the presentdisclosure.

DETAILED DESCRIPTION

FIGS. 1A-B depict perspective and top views, respectively, of a switchmodule in accordance with an illustrative embodiment in accordance withthe present disclosure. Switch module 100 comprises switch 102 andhousing 104.

Switch 102 includes fiber-Bragg grating portions 106-1 and 106-2, pivotassembly 108, fiber-mounting disks 110-1 and 110-2, magnet holder 112,cables 114-1 and 114-2, pads 116, input port 118, output port 120, andexternal magnet EM1. In FIG. 1A, the switch module is depicted with thelid of housing 104 removed. In FIG. 1B, the switch module is depictedwithout housing 104 and external magnet EM1.

Housing 104 is an enclosure that surrounds switch 102 to protect it fromenvironmental degradation. In the depicted example, housing 104comprises aluminum; however, any suitable structural material can beused in housing 104, including, without limitation, polymers, ceramics,composite materials and the like.

FIG. 2 depicts operations of a method for forming a security switch inaccordance with the illustrative embodiment. Method 200 begins withoperation 201, wherein optical fiber 122 is provided.

Optical fiber 122 is a conventional single-mode optical fiber thatincludes fiber-Bragg grating (FBG) portions 106-1 and 106-2, each ofwhich includes an FBG. Optical fiber 106 guides light between input port118 and output port 120.

FIG. 3 depicts a cross-sectional view of a representative FBG portion.FBG portion 106 includes core 302, cladding 304, and FBG 306 and isrepresentative of each of FBG portions 106-1 and 106-2.

Core 302 comprises a light guiding material having a refractive index ofn1.

Cladding 304 is material that surrounds core 302, where this materialhas a refractive index of n2, which is lower than n1. As a result,cladding 304 confines the optical energy of a light signal propagatingthrough optical fiber 122 primarily to core 302.

FBG 306 is a periodic structure within optical fiber 106, which includesregions of features 308. Features 308 are written into the core ofoptical fiber 122 in conventional fashion such that each feature has arefractive index that is locally increased to n3, where n1<n3<n2.Features 308 are formed such that they are evenly spaced apart byunperturbed core material with Bragg-grating period A. FBG portion 106-1includes FBG 306-1 having period Λ1 and FBG portion 106-2 includes FBG306-2 having period Λ2.

Plot 310 depicts the variation of the refractive index of core 302 alongthe length of FBG portion 106.

Plots 312 and 314 show the transmission and reflection spectra,respectively, of FBG 306. As evinced by the plots, FBG 306 reflectslight having operating wavelength λ1 while passing other wavelengthssubstantially unperturbed. The value of operating wavelength λ1 is basedon the period, Λ, of FBG 306. As a result, a change in the length of FBGportion 106, will change grating period Λ, shifting operating wavelengthλ1.

At operation 202, optical fiber 122 is mounted in switch 102. Opticalfiber 122 is mounted is switch 102 such that FBG portions 106-1 and106-2 (referred to, collectively, as FBG portions 106) are held betweenpivot assembly 108 and fiber-mounting disks 110-1 and 110-2,respectively.

Pivot assembly 108 is a mechanical fixture that includes bearing 124A,which rides on shaft 124B, thereby enabling the pivot assembly to rotateabout rotation axis A1. In the depicted example, bearing 124A is apress-fit polymer bearing; however, other bearings (e.g., sleevebearings, etc.) can be used without departing from the scope of thepresent disclosure. Pivot assembly 108 also includes attachment points126-1 and 126-2, which rotate about rotation axis A1 with the pivotassembly.

In the depicted example, FBG 106-1 is located between fiber-mountingdisk 110-1 and attachment point 126-1, and FBG 106-2 is located betweenfiber-mounting disk 110-2 and attachment point 126-2. In the depictedexample, optical fiber 122 is rigidly attached to the fiber-mountingdisks and attachment points using glass solder. In some embodiments, adifferent conventional method (e.g., crimping, epoxy, metals solder,etc.) is used to attach optical fiber 122 to at least one of theattachment points and fiber-mounting disks.

It should be noted that, preferably, optical fiber is arranged withinswitch 102 such that switch module 100 is polarization independent,thereby enabling interchangeability of input port 118 and output port120.

At optional operation 203, tension is induced in FBG portions 106.Preferably, the tension induce in FBG portions 106 is substantiallyequal; however, unequal tensions can also be used. Applying apre-tension in FBG portions 106 establishes a baseline strain thatfacilitates operation.

The tension in FBG portions 106-1 and 106-2 is controlled by tensionassemblies TA1 and TA2, respectively, each of which includes an arm 132,a pin 134, and an adjustment screw 130.

Arms 132-1 and 132-2 are rigid members that are configured to rotateabout pins 134-1 and 134-2, respectively. Arm 132-1 includes a fibermounting disk 110-1, which rigidly clamps an end of FBG portion 106-1.When adjustment screw 130-1 is tightened, it pushes fiber-mounting disk110-1 away from pivot assembly 108, thereby increasing the tension inFBG portion 106-1. In similar fashion, arm 132-2 includes a fibermounting disk 110-2, which rigidly clamps one end of FBG portion 106-2.When adjustment screw 130-2 is tightened, the adjustment screw pushesfiber-mounting disk 110-2 away from pivot assembly 108 and the tensionin FBG portion 106-2 is increased.

At operation 204, permanent magnets 128-1 and 128-2 are mounted inmagnet holder 112.

Magnet holder 112 is a rigid fixture that is attached to pivot assembly108 such that motion of magnet conventional permanent magnets 128-1 and128-2 rotates pivot assembly 108 about rotation axis A1. In the depictedexample, permanent magnets 128-1 and 128-2 are press-fit into oppositesides of magnet holder 112; however, any suitable method can be used toattach the permanent magnets to the magnetic holder without departingfrom the scope of the present disclosure.

Cables 114-1 and 114-2 are tactical or armored cables that areoptionally included in switch module 100 to protect optical fiber 122.

Pads 116 are optionally included in switch module 100 to limit the totalrange of motion of pivot assembly 108, as well as dampen the motion ofthe pivot assembly when switch 102 is tripped.

FIG. 4 depicts operations of a method for monitoring an access point inaccordance with the illustrative embodiment. In the depicted example,the access point is a doorway comprising a moving door and a stationarydoorframe; however other access points (e.g., windows, skylights, etc.)can be monitored without departing from the scope of the presentdisclosure. Furthermore, in some embodiments, switch module 100 is usedto monitor configurations other than access points, such as the positionof valuable items, such as equipment, computers, vehicles, etc.Operation 400 begins with operation 401, wherein external magnet EM1 ismounted to a stationary member of the access point. In the depictedexample, the access point is a doorway and the stationary member is aportion of its doorframe.

At operation 402, housing 104 is mounted to the door of the doorway suchthat surface A is in close proximity with external magnet EM1 andpermanent magnet 128-2 and external magnet EM1 are operatively (i.e.,magnetically) coupled. It should be noted that, in some embodiments,external magnet EM1 is not included and switch module 100 is mountedsuch that surface A is in close proximity to a different element, suchas a ferromagnetic metal element, etc., that is magnetically coupledwith permanent magnet 128-2. Furthermore, in some embodiments, housing104 is mounted to a stationary member and the element with which it ismagnetically coupled is mounted on a moving element of the access point.

When permanent magnet 128-2 and external magnet EM1 are magneticallycoupled, an attractive force between them arises causing permanentmagnet 128-2 to move toward surface A. The motion of the magnet rotatespivot assembly 108 clockwise about rotation axis A1, thereby increasingthe strain in FBG portion 106-1 while simultaneously reducing the strainin FBG portion 106-2.

As a result, grating period Λ1 of FBG 306-1 increases and grating periodΛ2 of FBG 306-2 decreases, thereby changing the spectral positions ofoperating wavelengths λ1-1 and λ1-2. These operating wavelengths remainconstant until switch 102 is actuated. In the depicted example, switch102 is armed by pre-tensioning FBG portions 106-1 and 106-2 to establishan initial separation of 1 nm between the FBG operating wavelengths whenpermanent magnet 128-2 and external magnet EM1 are magnetically coupled.

At operation 403, source 138 provides light signal 136 to input port118.

Source 138 is a conventional light source operative for providing lightsignal 136 such that its spectrum includes operating wavelengths λ1-1and λ1-2.

At operation 404, receiver 140 receives light signal 138 from outputport 120.

Receiver 140 is a conventional optical detection system operative fordetecting light whose spectral content includes operating wavelengthsλ1-1 and λ1-2. Receiver 140 provides detection signal 142 to processor134, where the detection signal includes the spectral positions ofoperating wavelengths λ1-1 and λ1-2. In some embodiments, detectionsignal 142 includes the magnitude of light at one or both of operatingwavelengths λ1-1 and λ1-2.

Processor 134 is a conventional processor that is operative for, amongother things, processing detection signal 142 and issuing an alert whenactuation of switch 102 is detected.

At operation 405, processor 134 compares a parameter of detection signal142 to an actuation threshold. In the depicted example, the parametermonitored is the separation between operating wavelengths λ1-1 and λ1-2and the actuation threshold is a difference of 2 nm between operatingwavelengths λ1-1 and λ1-2. In some embodiments, the actuation thresholdis a predetermined magnitude change in the intensity of light at one orboth of operating wavelengths λ1-1 and λ1-2.

Switch 102 actuates when the separation between permanent magnet 128-2and external magnet EM1 changes as a result of movement of the door onwhich housing 104 is mounted. This change in separation reduces themagnetic force between permanent magnet 128-2 and external magnet EM1and pivot assembly 108 rotates counter-clockwise. As a result, gratingperiod Λ1 of FBG 306-1 decreases while grating period Λ2 of FBG 306-2realizing equal and opposite wavelength shifts of operating wavelengthsλ1-1 and λ1-2.

At operation 406, if the monitored parameter exceeds the actuationthreshold, processor 134 issues an alarm signal that indicates switch102 has been actuated.

It should be noted that, because pivot assembly 108 includes a magnet onboth sides, both of sides A and B can be monitored with switch module100. In some embodiments, pivot assembly 108 includes only one magnetand, therefore, only one of sides A and B can be monitored. In someembodiments, pivot assembly 108 is configured in a different shape(e.g., an L shape) such that a permanent magnet 128 is adjacent to andpoints toward surface C of housing 104.

In some embodiments, adjustment screws 124, arms 126, and pins 128 arenot included and, therefore, FBG portions 122-1 and 122-2 are not presetto a desired tension level. In such embodiments, the FBGs will havewhatever operating wavelengths arise due stress induced duringpackaging. By measuring each operating wavelength at installation,however, a baseline difference is established. Actuation in suchembodiments is detected when the operating-wavelength difference changesmore than the actuation threshold, as described above.

It should be noted that the use of two FBGs as described above and withrespect to switch module 100 is preferable because it provides a measureof tolerance to temperature variation for the switch module because atemperature change affects the operating wavelength of each FBGsubstantially equally. As a result, the operating-wavelength differenceremains substantially constant regardless of changes in ambienttemperature.

FIG. 5 depicts a schematic drawing of a top view of a switch module inaccordance with an alternative embodiment in accordance with the presentdisclosure. Switch module 500 comprises switch 502 and housing 104.

Switch 502 is analogous to switch 102; however, switch 502 includes onlyone fiber-Bragg grating portion—FBG portion 106-1. In addition, switch502 includes optical port 504, which functions as both input and outputport for the switch.

Optical fiber 506 is analogous to a portion of optical fiber 122 asdescribed above.

Light signal 136 is injected into optical fiber 506 at optical port 504.

Reflection signal 508 is received from FBG portion 106-1 at optical port504.

Actuation of switch 502 is detected by detecting a step function in theoperating wavelength of FBG 306-1 contained in reflection signal 508.Unfortunately, ambient-temperature changes can cause a slow drift in theFBG operating wavelength. As a result, switch 502 substantially constantmonitoring to determine its state. In some embodiments, actuation ofswitch 502 is detected by detecting a change in the magnitude of lightat a wavelength, such as the operating wavelength, in reflection signal508.

It should be noted that switch modules in accordance with the presentdisclosure have significant advantages over prior-art security switches,including the ability to:

-   -   i. operate in “electrical noisy” environments without        interference or signal degradation because they rely on only        optical signals; or    -   ii. operate over long distance—up to many kilometers from a base        station used to interrogation them; or    -   iii. be “daisy changed” with other switches, switch modules,        and/or optical sensors, thereby reducing the cost of system        installation; or    -   iv. operate in potentially explosive atmospheres because they        operate with low-power optical signals    -   v. any combination of i, ii, iii, and iv.

Furthermore, in some embodiments, switch modules in accordance with thepresent disclosure are substantially corrosion resistant, non-contact,and totally enclosed. As a result, the reliability of such switchmodules is improved—particularly for long-term sensing applications inextreme environments, due to the absence of any through-the-wall shafts,levers, or cams that could otherwise give rise to a jam of the switch.

Still further, switch modules in accordance with the present disclosureare very difficult to defeat. If the optical fiber is cut, the signal islost. In the case of a switch module having two FBGs, no prior knowledgeof the state of the switch module is required after a power outage todetermine the state of the switch module when the power is restored.

One skilled in the art will recognize, after reading this Specification,that each FBG in a daisy-chain configuration preferably operates at adifferent wavelength. In some embodiments, the operating wavelength ofeach FBG is known at installation, which enables each switch module aunique identifier that facilitates locating the precise location ofwhere access to a facility has occurred.

It is to be understood that the disclosure teaches just some examples ofembodiments and that many variations can easily be devised by thoseskilled in the art after reading this disclosure without departing fromits scope and that the scope of the present invention is to bedetermined by the following claims.

What is claimed is:
 1. A switch module comprising: a first fiber-Bragggrating (FBG) portion that includes a first FBG characterized by a firstoperating wavelength, wherein the first FBG portion has a first length,and wherein the first operating wavelength is based on the first length;and a first magnet that is mechanically coupled with the first FBGportion such that a first motion of the first magnet induces a firstchange in the first operating wavelength.
 2. The switch module of claim1 further comprising: a housing that contains the first FBG portion andthe first magnet; and a ferromagnetic element that is external to thehousing; wherein the ferromagnetic element and the first magnet areconfigured such that (1) the magnetic coupling between them is based ona first separation between the housing and the ferromagnetic element and(2) a change in the first separation induces the first motion.
 3. Theswitch module of claim 2 further comprising: a second FBG portion thatincludes a second FBG characterized by a second operating wavelength,wherein the second FBG portion has a second length, and wherein thesecond operating wavelength is based on the second length; a pivotassembly that includes a first attachment point and a second attachmentpoint, wherein the pivot assembly is mechanically coupled with the firstmagnet such that the first motion induces a first rotation of the firstand second attachment points about a rotation axis; a third attachmentpoint; and a fourth attachment point; wherein the first FBG portion isaffixed to each of the first attachment point and the third attachmentpoint, and wherein a first separation between the first and the thirdattachment points defines the first length; wherein the second FBGportion is affixed to each of the second attachment point and the fourthattachment point, and wherein a second separation between the second andthe fourth attachment points defines the second length; and wherein thefirst rotation increases the first length and decreases the secondlength.
 4. The switch module of claim 3 wherein the first rotationincreases the first length and decreases the second length by the samemagnitude.
 5. The switch module of claim 3 further comprising: a firsttension assembly that is configured to control the tension in the firstFBG portion; and a second tension assembly that is configured to controlthe tension in the second FBG portion.
 6. The switch module of claim 1further comprising: a pivot assembly that includes a first attachmentpoint, wherein the pivot assembly is mechanically coupled with the firstmagnet such that the first motion induces a first rotation of the firstattachment point about a rotation axis; and a second attachment point;wherein the first FBG portion is affixed to each of the first attachmentpoint and the second attachment point, and wherein a first separationbetween the first and the second attachment points defines the firstlength.
 7. The switch module of claim 6 further comprising a tensionassembly that is configured to control the tension in the first FBGportion.
 8. The switch module of claim 1 further comprising: a sourcefor providing a first light signal to the first FBG grating, the firstlight signal having a spectral range that includes the first operatingwavelength; a receiver for detecting a second light signal received fromthe first FBG grating, the second light signal being characterized bythe first operating wavelength, wherein the second light signal includesat least a portion of the first light signal; and a processor formonitoring a parameter of the second light signal, wherein the parameteris selected from the group consisting of spectral position andmagnitude.
 9. A switch module comprising: (1) a housing; and (2) aswitch that is contained within the housing, wherein the switchincludes: (i) a first fiber-Bragg grating (FBG) portion that includes afirst FBG characterized by a first operating wavelength, wherein thefirst FBG portion has a first length that extends between a firstattachment point and a second attachment point, and wherein the firstoperating wavelength is based on the first length; (ii) a pivot assemblythat includes the first attachment point; and (iii) a first magnet thatis mechanically coupled with the pivot assembly such that a first motionof the first magnet rotates the first attachment point about a rotationaxis and induces a first change in the first length.
 10. The switchmodule of claim 9 further comprising (3) a tension assembly that isconfigured to control the tension in the first FBG portion.
 11. Theswitch module of claim 9 further comprising: (3) a source for providinga first light signal to the first FBG grating, the first light signalhaving a spectral range that includes the first operating wavelength;(4) a receiver for detecting a second light signal received from thefirst FBG grating, the second light signal being characterized by thefirst operating wavelength, wherein the second light signal includes atleast a portion of the first light signal; and (5) a processor formonitoring a parameter of the second light signal, wherein the parameteris selected from the group consisting of spectral position andmagnitude.
 12. The switch module of claim 9 wherein the switch furthercomprises: (iv) a second FBG portion that includes a second FBGcharacterized by a second operating wavelength, wherein the second FBGportion has a second length that extends between a third attachmentpoint and a fourth attachment point, and wherein the second operatingwavelength is based on the second length; wherein the pivot assemblyincludes the third attachment point; and wherein the first motionrotates the third attachment point about the rotation axis and induces asecond change in the second length.
 13. The switch module of claim 12wherein the first change and second change are equal and opposite.
 14. Amethod comprising: (1) providing a switch by operations that include:(i) attaching a first fiber-Bragg grating (FBG) portion that includes afirst FBG characterized by a first operating wavelength to a firstattachment point and a second attachment point, wherein the first FBGportion is mounted such that it has a first length defined by theseparation between the first and second attachment points, and whereinthe first operating wavelength is based on the first length; and (ii)providing a first magnet that is mechanically coupled with the firstattachment point such that a first motion of the first magnet induces afirst change in the first length.
 15. The method of claim 14 furthercomprising (2) inducing a first pre-tension in the first FBG portion bymoving the second attachment point to change the first length.
 16. Themethod of claim 14 further comprising: (2) locating the switch on afirst element such that the first motion is induced by a second motionof one of the first element and a second element relative to the otherone of the first and second elements; (3) conveying a first light signalthrough the first FBG portion, wherein the first light signal includesthe first operating wavelength; and (4) monitoring a first parameter ofa second light signal characterized by the first operating wavelength,wherein the second light signal includes at least a portion of the firstlight signal.
 17. The method of claim 16 wherein the first parameter isthe spectral position of the first operating wavelength.
 18. The methodof claim 16 wherein the first parameter is the magnitude of the secondlight signal.
 19. The method of claim 14 further comprising (2) inducinga second change in the first length by moving the second attachmentpoint.
 20. The method of claim 14 wherein the switch is provided byoperations that further include (iii) providing a pivot assembly thatincludes the first attachment point, wherein the first magnet ismechanically coupled with the first attachment point via the pivotassembly such that the first motion induces a rotation of the firstattachment point about a first rotation axis.